This application is based on and hereby claims priority to German Application No. 10106821.2 filed on Feb. 14, 2001 and European Application No. 01103432.9 filed on Feb. 14, 2001, the contents of which are hereby incorporated by reference.
The invention relates to an arrangement for a mobile radio system having a base station with n outputs whose signals have essentially the same frequency and amplitude, and an antenna device.
The article xe2x80x9cAn Overview of Smart Antenna Technology for Mobile Communications Systemsxe2x80x9d from IEEE Communications Surveys, Fourth Quarter 1999, Vol. 2, No. 4 discloses base stations with n ports in which the signals which occur there are preferably used for the operation of an adaptive antenna arrangement which is composed of n individual antennas.
Here, for example in the case of transmission, a signal to be transmitted is divided within the base station in such a way that the n ports of the base station have essentially the same amplitude and frequency with different phase angles. Each of these signals is passed on to an individual antenna of an adaptive antenna arrangement and irradiated as a transmission signal. As a result of the different phase angles of the individual signals of the base station, and thus of the transmission signals of the individual antennas, a composite radiation diagram of the adaptive antenna arrangement is formed which has a preferential spatial direction.
As a result of the number n of the individual antennas of the adaptive antenna arrangement, it is possible to shape the composite radiation diagram of the adaptive antenna. As a result of the selection of different carrier frequencies and of the phase angles between the signals of the base station, it is possible to generate a plurality of mutually independent composite radiation diagrams of the adaptive antenna arrangement, each individual diagram of which has its own preferential spatial direction. The capacity of a radio network can be increased in this way.
The dimensions of an adaptive antenna arrangement are frequency-dependent and typically occur within the range from approximately 0.5 to 1.5 m in width and in the range of approximately 0.5 to 1.5 m in height. However, some preferred locations for antennas are not suitable for adaptive antenna arrangements of this size. If a location for an antenna is situated, for example, on an historical building, it can often not be used as a location for such large antenna arrangements for aesthetic reasons or because of laws protecting historical buildings. The statistics of the locations for antennas, which are only available in limited numbers, often prohibit the use of an adaptive antenna arrangement, for example owing to the wind load or the weight of the antenna arrangement.
For this reason, generally relatively small, and thus less conspicuous, individual antennas are provided for use at these locations. However, for such antennas it would be necessary to develop and produce individual base stations which would have to be suitable for the operation of non-adaptive antennas. As a result of the often only small production numbers, this would lead to an increased level of expenditure on development and fabrication.
Therefore, one object of the present invention is to adapt a base station with n ports whose signals have essentially the same frequency and amplitude to a non-adaptive antenna device.
The invention comprises two preferred arrangements for a mobile radio system having a base station and having an antenna device.
In a first preferred arrangement, the base station is composed of n ports which are decoupled from one another and to which signals which have essentially the same frequency and amplitude but different phase angles are fed.
The base station contains a digital signal controller which, in the case of transmission, divides a digital signal to be transmitted into n individual digital signals which have essentially the same amplitude and frequency but have different phase angles, and which, in the case of reception, forms a composite reception signal with a uniform phase angle from the n individual signals.
The base station also contains a device for converting, in the case of transmission, these n individual signals of the signal controller into n analog, carrier-frequency radio signals for the n ports of the base station which are decoupled from one another. In the case of reception, the n analog, carrier-frequency radio signals are converted in the opposite direction into the n digital individual signals which have essentially the same amplitude and frequency but different phase angles, and which are then fed to the digital signal controller.
In order to connect this base station to a non-adaptive antenna device, a device for combining or dividing is arranged between the base station and the antenna device, which device for combining or dividing connects to one another, in the case of transmission, the radio signals which occur at the n ports of the base station and which have essentially the same amplitude and frequency but different phase angles, in such a way that a composite signal which occurs at one of the ports of the device for combining or dividing and has a uniform phase angle is produced and is fed as an antenna signal to the antenna device, and which device for combining or dividing divides, in the case of reception, the antenna signal of the antenna device, said signal being fed as a composite signal with uniform phase angle to the device for combining or dividing, into the n radio signals which have essentially the same frequency and amplitude but different phase angles and which are then fed to the n ports of the base station.
The device for combining or dividing advantageously contains a Butler matrix which has n ports for the radio signals of the base station and m ports for the antenna signals or composite signals, the composite signal or the antenna signal being fed to just one of the m ports and all the other m ports each being terminated with a terminating resistor. A Butler matrix of the type described here is known, for example, from the xe2x80x9cTaschenbuch der Hochfrequenztechnikxe2x80x9d by Meinke-Gundlach, fourth edition, year of publication 1986.
The radio signals of the base station advantageously have an essentially linearly rising phase angle with respect to one another.
In a second preferred arrangement for a mobile radio system having a base station and having an antenna device, the base station has n ports which are decoupled from one another and to which signals which have essentially the same frequency, amplitude and phase angle are fed.
The base station contains a digital signal controller which, in the case of transmission, divides a digital signal to be transmitted into n individual digital signals which have essentially the same amplitude, frequency and phase angle and which, in the case of reception, forms a composite reception signal with a uniform phase angle from the n individual signals.
The base station contains here a device for converting, in the case of transmission, the n individual signals of the signal controller into n analog, carrier-frequency radio signals for the n ports of the base station which are decoupled from one another. In the case of reception, the n analog, carrier-frequency radio signals which are fed to the n ports of the base station which are decoupled from one another are converted into the n individual digital signals and fed to the signal controller. The conversion is carried out using digital/analog converters and modulating and mixing devices, and with filters.
In order to connect the base station to a non-adaptive antenna device, a device for combining or dividing is arranged between the base station and the antenna device, which device for combining or dividing connects to one another, in the case of transmission, the radio signals which occur at the n ports of the base station and which have essentially the same amplitude, frequency and phase angle, in such a way that a composite signal which occurs at one of the ports of the device for combining or dividing and has a uniform phase angle is produced and is fed as an antenna signal to the antenna device, and which device for combining or dividing divides, in the case of reception, the antenna signal of the antenna device, said signal being fed as a composite signal with uniform phase angle to the device for combining or dividing, into the n radio signals which have essentially the same frequency, amplitude and phase angle and passes them on to the n ports of the base station.
In a preferred embodiment, the device for combining or dividing contains at least one Wilkinson combiner, which is known, for example, from the book xe2x80x9cRF Design Guidexe2x80x9d by Peter Vizmuller, year of publication 1995.
In the two preferred arrangements described, the antenna device contains just one port at which the antenna signal or the composite signal is present. In this context, the antenna device can be implemented either as an individual antenna or as a group antenna.
The invention adapts a base station, which has n decoupled ports whose signals have essentially the same amplitude and frequency, to a non-adaptive antenna device. This avoids the need for a further fabrication line for base stations which would have to be specially developed for the operation of a non-adaptive antenna.
If, as in the reception case described above, an antenna signal is divided into n analog, carrier-frequency radio signals, processed and combined again, the signal-to-noise ratio is typically improved by a factor of two as a result of the coherent combination of the individual signals.
As a result of the preferred use a Butler matrix or at least one xe2x80x9cWilkinson combinerxe2x80x9d the individual signals are combined and respectively divided essentially without loss.
As a result of the combination of n carrier-frequency individual signals to form a composite signal in the case of transmission, relatively small gain factors may be used for the individual signals. The power amplifiers used typically have linear gain characteristic curves here, as a result of which interference frequencies within the mobile radio system are avoided.